Rapid Summer Death of Shrubs - Collar Rot

Q. We have two 12-year-old Texas Sage shrubs concealing the street mailboxes. Within a month this past summer, they were dying back rapidly. The dieback spread over both plants. The irrigation hasn’t changed. Any idea what could be causing this? 

Not readers plant. Showing collar rot. The top dies because its choked....rotten.

A. My explanation follows the KISS principle. Texas Sage, a Chihuahuan desert native, has roots that die if watered too often. If the main stem or trunk of this shrub stays wet, this could cause it to die. My guess this is a trunk/root disease caused by watering too often. This disease moves with irrigation water and can spread easily between nearby plants.

Put Emitters Close When First Planted

When first planted, the drip emitters must be close to the plant. I like to put them up to about 12 inches during the first year. They should be moved, and more drip emitters added, as the plant gets larger in the second or third year. They are moved to about 12 to 18 inches away from the trunk at this time. This practice does not change the irrigation frequency but changes how much water is applied and where it is applied. A larger area under the plant is watered to compensate for its increased size.

            Move the drip emitters away from the trunk or main stem to a distance of 12 to 18 inches from its trunk. This should be done when the shrub is 2 to 4 years in the ground. At the same time, add more drip emitters and redistribute the emitters so that they irrigate half the area under the enlarged plant canopy. This gives the plant more water, distributes the water to a larger area because it’s larger and reduces the chance of trunk/root diseases of susceptible plants.